The present invention relates to electrical resistance heating apparatus and more particularly to heating jackets suitable for use in clean room environments and to the heating elements employed therein.
It has been found that in processing semiconductor wafers, it is advantageous to heat portions of the process equipment located downstream, and possibly upstream, of a horizontal diffusion-type chemical vapor deposition (CVD) chamber. In this manner, the condensation of compounds such as silicon nitride, ammonium and dichloroxylene from a gaseous to a crystalline state is avoided or substantially reduced, thereby assisting in their recapture and/or further availability for ongoing process reactions. Heating jackets disposed in surrounding relation to the CVD chamber are well known; however, due to their high heating capacity and cumbersomeness, these jackets are not well suited for use on outlying pipes and other vessels where heating requirements are more moderate and where there is a need to install and remove the jacket relatively quickly. In addition, there may be several vessels connected either directly or indirectly to the primary CVD chamber, so the cost of covering these outlying structures with high capacity heating jackets could be prohibitive. Thus, there was a need for a relatively modest heating jacket in terms of heating capacity and cost, as well as one which was easily installed and removed.
Heretofore, moderate range heating jackets which might otherwise satisfy the foregoing need have contained a substantial amount of fiberglass and/or have tended to carry a static surface charge. These conventional moderate range heating jackets were unsuited for use with semiconductor processing equipment due to their tendency to introduce an unacceptable level of particles or fibers into the surroundings. Thus, there was a need for a heating jacket comprising static-dissipative, generally particle-free materials suitable for use in a clean room environment.
In addition, the heating elements employed in conventional moderate range jackets were typically ungrounded. However, NST Standards now require, or are expected to soon require, heating elements adapted for use in semiconductor production and other industrial processes to be fully or continuously grounded. Thus, there was also a need to devise a grounded heating element suitable for use in a moderate range heating jacket.